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lmv7251/lmv7255 1.8v low voltage comparator with rail-to-rail input general description the lmv7251/lmv7255 are rail-to-rail input low voltage comparators, which can operate at supply voltage range of 1.8v to 5.0v. the lmv7251/lmv7255 are available in space saving sc-70 or sot23-5 packages. these comparators are ideal for low voltage and space critical designs. the lmv7251 features a push-pull output stage. this feature allows operation with minimum power consumption when driving a load. the lmv7255 features an open drain output. this allows the connection of an external resistor at the output. the output of the comparator can be used as a level shifter. the ic's are built with national semiconductor's advance submicron silicon-gate bicmos process. the lmv7251/lmv7255 have bipolar inputs for improved noise performance and cmos outputs for better rail-to-rail output performance. features (v s = 1.8v, t a = 25c, typical values unless specified). n single or dual supplies n low supply voltage 1.8v to 5.0v n ultra low supply current 11a n low input bias current 14na n low input offset current 200pa n low input offset voltage +/?0.3mv n response time 670ns (20mv overdrive) n input common mode voltage 0.1v beyond rails applications n mobile communications n laptops and pda's n battery powered electronics n general purpose low voltage applications typical circuit connection diagram ds200057-2 figure 1. threshold detector ds200057-1 top view january 2001 lmv7251/lmv7255 1.8v low voltage comparator with rail-to-rail input ? 2001 national semiconductor corporation ds200057 www.national.com
absolute maximum ratings (note 1) if military/aerospace specified devices are required, please contact the national semiconductor sales office/ distributors for availability and specifications. esd tolerance 1kv (note 2) 200v (note 6) v in differential +/?supply voltage supply voltage (v + -v ? ) 5.5v voltage at input/output pins v + +0.1v, v ? ?0.1v soldering information infrared or convection (20 sec.) 235c wave soldering (10 sec.) 260c storage temperature range ?65c to +150c junction temperature (note 4) +150c operating ratings (note 1) supply voltage v + 1.8v to 5.0v junction temperature range (note 3) ?40c to +85c package thermal resisance (note 3) sot23-5 325c/w sc-70 265c/w 1.8v electrical characteristics unless otherwise specified, all limits guaranteed for t j = 25c, v + = 1.8v, v ? = 0v. boldface limits apply at the temperature extremes. symbol parameter condition typ (note 4) limits (note 5) units v os input offset voltage 0.3 6 8 mv max tc v os input offset average drift v cm = 0.9v (note 7) 10 uv/c i b input bias current 14 na i os input offset current 200 pa i s supply current 11 15 17 a max i sc output short circuit current sourcing, v o = 0.9v (lmv7251 only) 84 ma min sinking, v o = 0.9v 11.6 5 i leakage output leakage current v o = 1.8v (lmv7255 only) 300 pa v oh output voltage high i o = 1.5ma (lmv7251 only) 1.72 1.675 v min v ol output voltage low i o = ?1.5ma 65 125 mv max v cm input common voltage range cmrr > 45 db 1.9 v max ?0.1 v min cmrr common mode rejection ratio 0 < v cm < 1.8v 72 47 db min psrr power supply rejection ratio v + = 1.8v to 5v 79 55 db min 1.8v ac electrical characteristics unless otherwise specified, all limits guaranteed for t j = 25c, v + = 1.8v, v ? = 0v, v cm = 0.5v, v o =v + /2. boldface limits apply at the temperature extremes. symbol parameter condition typ (note 5) limits (note 6) units t phl propagation delay (high to low) input overdrive = 20mv load = 50pf//5k w 720 ns input overdrive = 50mv load = 50pf//5k w 380 ns lmv7251/lmv7255 www.national.com 2
1.8v ac electrical characteristics (continued) unless otherwise specified, all limits guaranteed for t j = 25c, v + = 1.8v, v ? = 0v, v cm = 0.5v, v o =v + /2. boldface limits apply at the temperature extremes. symbol parameter condition typ (note 5) limits (note 6) units t plh propagation delay (low to high) input overdrive = 20mv load = 50pf//5k w 670 ns input overdrive = 50mv load = 50pf//5k w 400 ns 2.7v electrical characteristics unless otherwise specified, all limits guaranteed for t j = 25c, v + = 2.7v, v ? = 0v. boldface limits apply at the temperature extremes. symbol parameter conditions typ (note 5) limits (note 6) units v os input offset voltage 0.03 6 8 mv max tc v os input offset average drift v cm = 1.35v (note 7) 10 v/c i b input bias current 15 na i os input offset current 210 pa i s supply current 11 18 22 a max i sc output short circuit current sourcing, v o = 1.35v (lmv7251 only) 28 15 ma sinking, v o = 1.35v 28 15 i leakage output leakage current v o = 2.7v, (lmv7255 only) 320 pa v oh output voltage high i o = 2ma (lmv7251 only) 2.63 2.575 v min v ol output voltage low i o = ?2ma 61 125 mv max v cm input common voltage range cmrr > 45db 2.8 v max ?0.1 v min cmrr common mode rejection ratio 0 < v cm < 2.7v 75 46 db min psrr power supply rejection ratio v + = 1.8v to 5v 79 55 db min 2.7v ac electrical characteristics unless otherwise specified, all limits guaranteed for t j = 25c, v + = 2.7v, v ? = 0v. boldface limits apply at the temperature extremes. symbol parameter condition typ (note 5) limits (note 6) units t phl propagation delay (high to low) input overdrive = 20mv load = 50pf//5k w 830 ns input overdrive = 50mv load = 50pf//5k w 430 ns t plh propagation delay (low to high) input overdrive = 20mv load = 50pf//5k w 730 ns input overdrive = 50mv load = 50pf//5k w 410 ns lmv7251/lmv7255 www.national.com 3
5v electrical characteristics unless otherwise specified, all limits guaranteed for t j = 25c, v + = 5v, v ? = 0v. boldface limits apply at the temperature ex- tremes. symbol parameter conditions typ (note 5) limits (note 6) units v os input offset voltage 0.03 6 8 mv max tc v os input offset average drift v cm = 2.5v (note 7) 10 v/c i b input bias current 16 na i os input offset current 220 pa i s supply current 12 20 25 a max i sc output short circuit current sourcing, v o = 2.5v (lmv7251 only) 82 50 ma min sinking, v o = 2.5v 78 50 i leakage output leakage current v o = 5v, (lmv7255 only) 375 pa v oh output voltage high i o = 4ma 4.9 4.82 v min v ol output voltage low i o = ?4ma 90 180 mv max note 1: absolute maximum ratings indicate limits beyond which damage to the device may occur. operating ratings indicate conditions for which the device is intended to be functional, but specific performance is not guaranteed. for guaranteed specifications and the test conditions, see the electrical ch aracteristics. note 2: human body model, 1.5k w in series with 100pf. note 3: the maximum power dissipation is a function of t j(max) , q ja , and t a . the maximum allowable power dissipation at any ambient temperature is p d =(t j(max) -t a )/ q ja . all numbers apply for packages soldered directly into a pc board. note 4: typical values represent the most likely parametric norm. note 5: all limits are guaranteed by testing or statistical analysis. note 6: machine model, 0 w in series with 200pf. note 7: offset voltage average drift determined by dividing the change in v os at temperature extremes into the total temperature change. lmv7251/lmv7255 www.national.com 4
typical performance characteristics (t a = 25c, unless otherwise specified). short circuit current vs. supply voltage ds200057-3 supply current vs. supply voltage ds200057-4 output voltage vs. supply voltage ds200057-5 output voltage vs. supply voltage ds200057-6 output voltage vs. output current @ 1.8v supply voltage ds200057-7 output voltage vs. output current @ 1.8v supply voltage ds200057-8 lmv7251/lmv7255 www.national.com 5
typical performance characteristics (t a = 25c, unless otherwise specified). (continued) output voltage vs. output current @ 2.7v supply voltage ds200057-9 output voltage vs. output current @ 2.7v supply voltage ds200057-10 response time for various input overdrives - t plh ds200057-11 response time for various input overdrives - t phl ds200057-12 response time for various input overdrives - t plh ds200057-13 response time for various input overdrives - t phl ds200057-14 lmv7251/lmv7255 www.national.com 6
application info basic comparators a comparator is quite often used to convert an analog signal to a digital signal. the comparator compares an input volt- age (v in ) at the non-inverting pin to the reference voltage (v ref ) at the inverting pin. if v in is less than v ref the output (v o ) is low (v ol ). however, if v in is greater than v ref , the output voltage (v o ) is high (v oh ). hysteresis the basic comparator configuration may oscillate or produce a noisy output if the applied differential input is near the comparator's input offset voltage. this tends to occur when the voltage on the input is equal or very close to the other input voltage. adding hysteresis can prevent this problem. hysteresis creates two switching thresholds (one for the rising input voltage and the other for the falling input volt- age). hysteresis is the voltage difference between the two switching thresholds. when both inputs are nearly equal, hysteresis causes one input to effectively move quickly pass the other. thus, effectively moving the input out of region that oscillation may occur. hysteresis can easily be added to a comparator in a non-inverting configuration with two resistors and positive feedback figure 3 . the output will switch from low to high when v in rises up to v in1 , where v in1 is calculated by v in1 =(v ref (r1 + r2))/ r2 the output will switch from high to low when v in falls to v in2 , where v in2 is calculated by v in2 =(v ref (r1+r2)-v cc r1)/r2 the hysteresis is the difference between v in1 and v in2 . d v in =v in1 -v in2 = ((v ref (r1 + r2)) / r2) - ((v ref (r1 + r2)-v cc r1) / r2) = v cc r1/ r2. for an inverting configured comparator, hysteresis can be added with a three resistor network and positive feedback. when input voltage (v in ) at the inverting node is less than non-inverting node (v t ), the output is high. the equivalent circuit for the three resistor network is r1 in parallel with r3 and in series with r2. the lower threshold voltage v t1 is calculated by: v t1 = ((v cc r2) / ((r1 r3) / (r1+ r3)) + r2) when v in is greater than v t , the output voltage is low. the equivalent circuit for the three resistor network is r2 in parallel with r3 and in series with r1. the upper threshold voltage v t2 is calculated by: v t2 =v cc ((r2 r3) / (r2 + r3)) / ((r1 + ((r2 r3) / (r2 + r3)) the hysteresis is defined as d v in =v t1 -v t2 = ((v cc r2) / ((r1 r3) / (r1+ r3)) + r2) (v cc ((r2 r3) / (r2 + r3)) / ((r1 + ((r2 r3) / (r2 + r3))) lmv7251 ds200057-15 lmv7255 ds200057-16 input/output ds200057-17 figure 2. basic comparator ds200057-18 ds200057-19 figure 3. non-inverting comparator configuration e lmv7251 lmv7251/lmv7255 www.national.com 7
application info (continued) input stage the lmv7251 and lmv7255 have rail-to-rail input stages. the input common mode voltage range is from ?100mv to (v cc + 100mv). output stage the lmv7251 has a push-pull cmos output stage. large push-pull output drivers allows rail-to-rail output swings with load currents in the miliampere range. the lmv7255 has a open drain cmos output stage. this requires an external pull-up resistor connected between the positive supply voltage and the output. the external pull-up resistor should be high enough resistance so to avoid exces- sive power dissipation. in addition, the pull-up resistor should be low enough resistance to enable the comparator to switch with the load circuitry connected. power supply considerations the lmv7251/lmv7255 are well suited for many battery- powered applications. the lmv7251/lmv7255 can operate from single power supply of +1.8v to +5v. the device typi- cally consumes only 11a with a 2.7v supply. with a high power supply rejection ratio (psrr) of 79 db (typical), the comparator is well suited for operating under conditions of a decaying battery voltage. power supply decoupling is critical and improves stability. place decoupling capacitors 0.1f as close as possible to the v + pin. for split supply applications, place decoupling capacitors 0.1f on both the v + and v ? pins. the decoupling capacitors will help keep the comparator from oscillating under various load conditions. ds200057-20 ds200057-21 figure 4. inverting configured comparator e lmv7255 lmv7251/lmv7255 www.national.com 8
ordering information package ordering info pkg marking supplied as nsc drawing 5-pin sot23-5 lmv7251m5 c16a 1k units tape and reel mf05a lmv7251m5x c16a 3k units tape and reel lmv7255m5 c18a 1k units tape and reel lmv7255m5x c18a 3k units tape and reel 5-pin sc-70 lmv7251m7 c17 1k units tape and reel maa05a lmv7251m7x c17 3k units tape and reel lmv7255m7 c19 1k units tape and reel lmv7255m7x c19 3k units tape and reel lmv7251/lmv7255 www.national.com 9
physical dimensions inches (millimeters) unless otherwise noted 5-pin sc70-5 ns package number maa05a lmv7251/lmv7255 www.national.com 10
physical dimensions inches (millimeters) unless otherwise noted life support policy national's products are not authorized for use as critical components in life support devices or systems without the express written approval of the president and general counsel of national semiconductor corporation. as used herein: 1. life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 2. a critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. national semiconductor corporation americas tel: 1-800-272-9959 fax: 1-800-737-7018 email: support@nsc.com national semiconductor europe fax: +49 (0) 180-530 85 86 email: europe.support@nsc.com deutsch tel: +49 (0) 69 9508 6208 english tel: +44 (0) 870 24 0 2171 fran?ais tel: +33 (0) 1 41 91 8790 national semiconductor asia pacific customer response group tel: 65-2544466 fax: 65-2504466 email: ap.support@nsc.com national semiconductor japan ltd. tel: 81-3-5639-7560 fax: 81-3-5639-7507 www.national.com 5-pin sot23-5 ns package number mf05a lmv7251/lmv7255 1.8v low voltage comparator with rail-to-rail input national does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and national reserves the righ t at any time without notice to change said circuitry and specifications.

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